Light emitting diodes (LEDs) can be fabricated to generate light in different colors. For producing white light, various colors can be combined. One way of producing white light from an LED structure is to deposit a yellow phosphor over a blue LED. There are many ways to do this. One of the most common ways is to mix phosphor particles in an encapsulation material and coat it over the LED. Another way is electrophoretic deposition where phosphor particles are deposited directly onto LEDs.
White light is produced when some of the blue light that is allowed to leak through the phosphor layer combines with the yellow light.
Another way of producing white light is to combine red, green, and blue light. This can be achieved either through the use of red, green and blue LEDs or through blue LEDs with red and green phosphors.
LEDs, such as blue and UV GaN LEDs, vary slightly in color emission even in the same wafer. Applying the same phosphor coating to all LEDs will thus result in a range of color temperatures (i.e., correlated color temperature or CCT) due to the varying characteristics of the LEDs. Further, variations in the amount of phosphor in the coating will also undesirably increase the CCT range. As a result, the output color (e.g., CCT of white light) can vary greatly, even though the fabrication process is the same.
Known or common challenges with some of the above methods include: 1) complexity of the phosphor deposition process; and 2) variations in the amount of phosphor from LED to LED, resulting in inconsistent color temperatures.